Drashigs were one of the most dangerous predators in the universe.
Drashigs were massive snake-like creatures with six eyes on stalks, fanged mouths and segmented bodies with greenish brown skin. They also had a sparse covering of hair. Their hide was strong enough to withstand machine gun fire, but especially large amounts of damage could kill them. They were very strong and could burst through metal structures. (TV: Carnival of Monsters) They were descended from posthumans. (PROSE: Daring Initiation)
Drashigs were unintelligent but social. They hunted in packs of three and lived in colonies of twenty. When hunting or in pain, they emitted a chilling scream. Drashigs were omnivorous and would eat anything, including spaceships. They hunted by scent and they would never give up the hunt once they found a trail. On the other hand, they would follow the trail, even when the prey had doubled back or were right by them.
Drashigs lived in swamps. They could fully submerge themselves in deep water and use their eyes to look for prey without giving away their hiding place, allowing them to launch surprise attacks and to have a wider field of vision, even seeing behind their own heads. (TV: Carnival of Monsters)
In the far future, a posthuman Coterie became lost on a million-year mission, during which radiation affected their evolution by activating "a few forgotten DNA pathways". Little Brother Intrepid transported some of their eggs backwards through time to a prehistoric swamp. From there, the species continued to evolve for several million more years before becoming Drashigs. (PROSE: Daring Initiation)
Iris Wildthyme encountered Drashigs in a feeding frenzy on their swamp world. (PROSE: The Scarlet Empress) Iris once mentioned that she'd saved the Doctor from Drashigs on Qon-ti-jaqir. (PROSE: Verdigris)
When a battlethruster made an emergency landing on the satellite of Grundle, the Drashigs living there killed all fifty of the crew. The crew used weapons to defend themselves, but, save for a few scraps of the reactor venticle, the Drashigs consumed the ship. (TV: Carnival of Monsters)
To observe the outcome of Intrepid's first paradox, two elders of Faction Paradox came to a Drashig swamp and watched two of the creatures mating and being abducted for a miniaturised carnival. (PROSE: Daring Initiation)
A colony of Drashigs from Grundle's satellite were kept in Vorg's Miniscope. While wandering through the Miniscope, the Third Doctor and Jo Grant accidentally found themselves in the Drashig habitat. The Drashigs followed them through the Miniscope, attacking the human habitat and eventually escaping out into Inter Minor, where they killed Kalik and Orum, two Inter Minorian government officials. However, the escaped Drashigs were all killed by Vorg with the Eradicator. (TV: Carnival of Monsters)
To kill the Eighth Doctor, Ryoth used a Time Scoop to bring a Drashig to the Eye of Orion. He chose it as he deemed Drashigs invulnerable. The Fifth and Eighth Doctors built a Temporal Reverse Feedback Field that sent the Drashig to Ryoth's location, where it ate him and the Time Scoop. The Drashig was transmatted to the Death Zone where it was hoped it would kill the other "horrors there". (PROSE: The Eight Doctors)
Cortalian found some Drashigs in the swamp of a forgotten world and modified their biodata to make make a small army of advanced servitors and bodyguards. (PROSE: Daring Initiation, Going Once, Going Twice) These Servitors acted as security at the First Auction in Heaven. (PROSE: Going Once, Going Twice)